A television door intercom apparatus having a construction shown in a block diagram of FIG. 7 has been proposed in the past as a television door intercom apparatus of this kind.
The television door intercom apparatus shown in the drawing has a door intercom substation 501 installed at the entrance and including a control circuit (hereinafter called a “substation CPU) 510, a call button 511, a call detection circuit (hereinafter called a “substation call detection circuit) 512, a camera 513, a picture processing circuit 514, a picture modulation circuit 515, a substation microphone 516, a substation speaker 517, a communication circuit (hereinafter called a “substation communication circuit”) 518 and a transmission interface circuit (hereinafter called a “substation transmission I/F”) 519, and a residential master station 502 installed inside a house and including a control circuit (hereinafter called a “master station CPU) 520, a call detection circuit (hereinafter called a “master station call detection circuit) 521, a signal generator circuit 522, a picture demodulation circuit 523, a picture monitor 524, a communication on/off switch 525, a master station microphone 526, a master station speaker 527, a communication circuit (hereinafter called a “master station communication circuit”) 528 and a transmission interface circuit (hereinafter called a “master station transmission I/F”) 529. The door intercom substation 501 and the residential master station 502 are connected to each other through a transmission line L501 having two wires.
When a visitor at the entrance pushes down the call button 511 of the door intercom substation 501 to call a resident inside the house in the television door intercom apparatus having the construction described above, the substation call detection circuit 512 detects this operation and outputs a call signal. The call signal is transmitted to the master station CPU 520 through the substation CPU 510, the substation transmission I/F 519, the transmission line L501 and the master station transmission I/F 529 of the residential master station 502.
The master station CPU 520 of the residential master station 502 detects the call signal from the door intercom substation 501, outputs the call signal to the master station call detection circuit 521 and activates the picture demodulation circuit 523 and the picture monitor 524. The master station call detection circuit 521 detects the call of the visitor at the entrance on the basis of the call signal transmitted through the master station CPU 520 and activates the call signal generator circuit 522. The signal generator circuit 522 causes the master station speaker 527 to output call sound to notify the resident inside the house of the call.
The camera 513, the picture processing circuit 514 and the picture modulation circuit 515 of the door intercom substation 501 are operated under the control of the substation CPU 510 on the basis of power (not shown and not explained in detail) supplied through a reverse route of the call signal under the control of the master station CPU 520 of the residential master station 502 detecting the call signal. The picture of the visitor taken by the camera 513 is appropriately signal-processed (modulation, demodulation, etc) through the picture processing circuit 514, the picture modulation circuit 515, the substation transmission I/F 519, the transmission line L501, the master station transmission I/F 529 of the residential master station 502 and the picture demodulation circuit 523, and is displayed on the picture monitor 524.
The resident inside the house judges the visitor conducting the call operation at the entrance on the basis of the call sound from the master station speaker 527 and the picture displayed on the picture monitor 524 of the residential master station 502, and then pushes the communication on/off switch to establish the communication with the visitor (bi-directional communication by sound; not explained in detail).
In the television door intercom apparatus according to the prior art, however, a predetermined field-of-view angle is set to the camera 513 of the door intercom substation 501 for taking the picture of the visitor conducting the call operation at the entrance as shown in an operation explanatory view of FIG. 8. Therefore, when the visitor is intentionally or unintentionally out of the range of the field-of-view angle of the camera 513, the picture monitor 524 of the residential master station 502 cannot display the picture of the visitor or displays only a cut picture. Consequently, recognition performance for the resident who judges the visitor on the basis of this picture drops, and security of the resident who responds to a call of a stranger, for example, drops, too.